1. Field of the Invention
The present invention relates to a developing device in an image forming apparatus, which forms an image by means of an electro-photography by using charged toner, and more particularly to a method for supplying the toner to a supplying roller in the developing device.
2. Description of the Related Art
There are various types of developing devices used for an image forming apparatus such as a laser printer or the like. The developing device may be constructed to be integrated into a single unit and may be detachably mounted on the laser printer. Further, the developing device may be provided with a replaceable toner cartridge for retaining toner and may supply the toner from a toner supply port, which is composed of two toner supply holes i.e., a toner supply hole formed at a substantially central position in a width direction of the toner cartridge and a toner supply hole formed on a frame side.
For example, in the toner cartridge, there is an agitator for agitating the toner and then supplying the toner from the toner supply port to a side of a developing chamber. A toner supplying roller is rotatably disposed at the lower portion within the developing chamber, which is blocked by an upper frame and a lower frame. This toner supplying roller charges the toner supplied from the toner supply port with a predetermined polarity, and supplies the charged toner to a developing roller. The developing roller is disposed so as to be in contact with a photosensitive drum, on the surface of which an electro-static latent image is formed by an exposing device for scanning a laser light on the basis of image data. In operation, the developing roller supplies the toner to the electro-static latent image formed on the surface of the photosensitive drum to thereby perform a toner development of the image. Then, the image toner-developed on the surface of the photosensitive drum is transferred onto a paper transported from a paper transporting section, and accordingly the image is formed.
In the above mentioned toner cartridge, it is necessary to prevent the contamination at respective sections of the laser printer, since the toner is leaked out and dispersed when replacing the toner cartridge. Thus, the toner supply port is formed only at one position of a substantially central position in the width direction of the toner cartridge.
Hence, when the toner is supplied from the toner cartridge through the toner supply port to the developing chamber, the toner tend to stay at the central position of the toner supplying roller, in correspondence with the position of the toner supply port. This results in the shortage of the supply of the toner to both ends of the toner supplying roller. In such a case, the toner cannot be uniformly supplied and thus cannot be adhered to the whole toner supplying roller. Consequently, the toner cannot be uniformly supplied to the developing roller and the electro-static latent image on the photosensitive drum. This causes the density irregularity on the image formed on the paper such that the density is dense at the central position of the image and is light at both ends of the image. This results in a problem that the image with an excellent quality cannot be formed.
In order to solve the above mentioned problem, it may be considered to form the toner supply port in the whole width direction of the toner cartridge to thereby supply the toner to the whole toner supplying roller. However, in this case, the toner supplied to both ends of the toner supplying roller tends to stay at both ends of the toner supplying roller. At this time, the toner is used in an order starting from fresh toner, which is easy to be used for the development of the image. Hence, only the toner with poor quality, which is difficult to use for the development of the image, stay at both ends of the toner supplying roller. This results in a problem again that the image with the excellent quality cannot be formed.
The present invention is proposed in view of the above mentioned problems. It is therefore an object of the present invention to provide: a developing device in an image forming apparatus, in which fresh toner from a toner supply port can be uniformly adhered to a whole supplying roller and which can form an image having an excellent quality for a long term; and the image forming apparatus having the developing device.
The above object of the present invention can be achieved by a developing device in an image forming apparatus provided with: a developing roller opposed to a photosensitive body, on which an electro-static latent image is formed, for developing the electro-static latent image by using toner; a supplying roller for supplying the toner to the developing roller; a wall member prescribing a developing chamber, in which the developing roller and the supplying roller are disposed, and a toner supply port, through which the toner is supplied into the developing chamber; a pair of upper and lower auger members disposed in the developing chamber at a vicinity of the toner supply port for carrying and circulating the toner supplied through the toner supply port, and adhering the toner onto the supplying roller; and an auger partition plate disposed between the upper and lower auger members for restricting movements of the toner between the upper and lower auger members.
According to the developing device, the toner is supplied from a toner cartridge through the toner supply port into the developing chamber. Then, the toner in the developing chamber are carried and circulated by the upper and lower auger members, and are adhered onto the supplying roller. At this time, the movements of the toner between the upper and lower auger members are restricted by the auger partition plate. Then, the toner is supplied to the developing roller by the supplying roller. Finally, the electro-static latent image formed on the photosensitive body is developed by using the toner by the developing roller. Accordingly, by the upper and lower auger members and the auger partition plate, the circulation route of the toner is regulated so that the toner is smoothly carried and circulated in the developing chamber, and that the toner is prevented from partially staying in the developing chamber. Consequently, it is possible to almost always adhere the fresh toner uniformly onto the substantially whole area of the supplying roller, so that it is also possible to form the image having the high quality for a long term without the density irregularity by the image forming apparatus.
In one aspect of the developing device of the present invention, the toner supply port is formed at a central position in a lateral direction, which is parallel to rotational axes of the supplying roller and the developing roller, of the developing chamber, the lower auger member carries the toner from the toner supply port toward both end positions in the lateral direction of the developing chamber, the upper auger member carries the toner from the both end positions toward the toner supply port, and the auger partition plate has such a shape that the toner carried by the lower auger member can move through the auger partition plate at both ends thereof to the upper auger member.
According to this one aspect, in the developing chamber, the toner is carried from the toner supply port i.e. the central position toward the both end positions by the lower auger member. Then, the toner is carried from the both end positions toward the toner supply port i.e. the central position by the upper auger member. At this time, the toner carried by the lower auger member can move through the auger partition plate at both ends thereof to the upper auger member. In this manner, the toner is carried and circulated by the lower and upper auger members, while the movements of the toner at positions other than at both end positions are restricted by the auger partition plate. Therefore, it is possible to almost always adhere the fresh toner onto substantially the whole area of the supplying roller.
In this one aspect, the lower auger member may have spiral teeth formed from the central position toward both end positions, and the upper auger member may have spiral teeth formed from both end positions toward the central position. Thus, the toner can be carried and circulated by the spiral teeth of the lower and upper auger members.
In this one aspect also, the auger partition plate may have a portion prescribing a notch at the central position on a far side with respect to the toner supply port. Thus, after the toner is carried and circulated by the upper and lower auger members, while one portion of the toner is returned to the toner cartridge through the toner supply port, another portion of the toner is carried and circulated again through the notch of the auger partition plate at the central position in accordance with the amount of the toner. Therefore, it is possible to carry and circulate the toner efficiently without the sequestration of the toner in the developing chamber.
In this one aspect also, the auger partition plate may be shorter in the lateral direction than the lower and upper auger members. Thus, the toner can move between the lower and upper auger members at both end positions where the auger partition plate is absent.
In another aspect of the developing device of the present invention, the developing device is detachably mounted as one unit on the image forming apparatus.
According to this aspect, the installment, the maintenance and the exchange of the developing device can be easily performed by detaching and attaching the developing device as one unit.
The above object of the present invention can be also achieved by an image forming apparatus provided with: (a) a photosensitive body on which an electro-static latent image is formed, (b) the above described developing device of the present invention, (c) a latent image forming device for forming on the photosensitive body the electro-static latent image corresponding to an image to be recorded, (d) a transferring device for transferring the toner, which is adhered to the photosensitive body in correspondence with the formed electro-static latent image, onto a record paper on which the image is to be recorded, and (e) a fixing device for fixing the toner transferred on the record paper.
According to the image forming apparatus, the electro-static latent image is formed on the photosensitive body by the latent image forming device. Then, the latent image is developed by the aforementioned developing device of the present invention. Then, the developed image of the toner on the photosensitive body is transferred onto the record paper by the transferring device. Finally, the transferred image of the toner on the record paper is fixed by the fixing device. Thus, fresh toner is almost always adhered uniformly onto the substantially the whole area of the supplying roller in the developing device, so that it is possible to form the image having the high quality for a long term without the density irregularity.
In one aspect of the image forming apparatus of the present invention, the image forming apparatus is further provided with a toner cartridge for retaining the toner which has a wall member prescribing a toner supply hole, which fits with the toner supply port of said developing device.
According to this aspect, the toner can be supplied from the toner cartridge through the toner supply port, and one portion of the toner is returned to the toner cartridge through the toner supply port. Thus the supply and circulation of the toner in the developing chamber can be smoothly performed.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings briefly described below.